A demographic tidal wave helped President Barack Obama win a tight but decisive re-election victory Tuesday with record-breaking support from Hispanic voters, massive turnout from African-Americans and continuing enthusiasm from young Americans.

Although Republican nominee Mitt Romney won a larger share of the white vote than any presidential candidate since Ronald Reagan scored a landslide re-election in 1984, the former Massachusetts governor ended up a loser at the polls because of the racial, ethnic and generational changes that have altered the U.S. electoral landscape.

“We are an American family and we rise and fall together as one nation and one people,” Obama said in a victory speech that sought common ground with the Republican he defeated and unity for a deeply divided nation. “These arguments we have are a mark of our liberty.”

With more than 85 percent of the votes counted nationwide early Wednesday morning, Obama led Romney by 50 percent to 49 percent in the popular vote. But Obama already had won enough states to clinch the 270 electoral votes needed to secure re-election.

In a gracious concession speech delivered, a subdued Romney called on disappointed Republicans to “earnestly pray” for Obama to succeed.

“This is a time of great challenge for America, and I pray that the president will be successful in guiding our nation,” the GOP nominee told a quiet crowd in Boston.

Obama’s challenges include tackling a stubbornly high unemployment rate, a slow-growth recovery, record-breaking federal deficits and a burgeoning national debt. He also will preside over implementation of the controversial health-reform law approved by Congress in 2010 and due to take effect fully in 2014.

“While our road has been hard, while our journey has been long, we have picked ourselves up, we have fought our way back, and we know in our hearts that for the United States of America, the best is yet to come,” Obama told supporters in his hometown of Chicago.

To succeed, Obama will need to break through partisan polarization that was reflected Tuesday at the polls. The president received the support of 92 percent of Democrats and 86 percent of liberals, while Romney was backed by 94 percent of Republicans and 83 percent of conservatives.

Romney ran up large majorities in heavily Republican states, but the GOP nominee couldn’t dent Obama’s Midwestern firewall and fell short in other targeted states across the nation, including Virginia, Florida, Colorado, Nevada and New Hampshire.

Obama’s electoral vote landslide is a reflection of the changing face of America. The portion of nonwhite voters in the electorate has tripled over the last four decades to 28 percent on Tuesday. The Democratic incumbent led among African Americans by 93 percent to 7 percent – the best performance by a Democrat since Lyndon Johnson in 1964.

Heavy African American turnout in Philadelphia, Detroit, Cleveland, Cincinnati, Richmond and Miami changed the dynamic in five battleground states. In key swing states, Romney received just 1 percent of the African American vote in Florida and 3 percent in Ohio and Virginia.

Meanwhile, Latino voters, energized by tough Republican rhetoric on immigration, voted Democratic by 69 percent to 30 percent, tipping the balance of power in a string of states including Florida, Nevada, New Mexico and Colorado.

“Gov. Romney’s shift to the right on the issue of immigration during the GOP primary season made it impossible for him to equal the number of Latino votes that George W. Bush received in 2000 and 2004,” said Aaron Kall, director of debate at the University of Michigan. “Efforts by numerous states to curtail early voting and require photo identification seem to have motivated these groups to record turnout numbers.”

In addition to minority voters, Obama’s majority-making coalition included young voters, highly educated citizens and women.

For the first time in American history, Latinos made up 10 percent of the electorate, up from 9 percent in 2008. The overwhelming Hispanic support – and strong turnout — helped Obama win New Mexico and Iowa, and kept the race close in states such as Florida, Colorado and Virginia.

In contrast to Obama’s rainbow coalition, Romney’s core supporters were older, evangelical and white. Among white voters, the Republican nominee topped Obama by 20 points, 59 percent to 39 percent. Romney scored particularly well among older white men, white women who have not completed college and rural white males.

“We’re seeing a Republican party whose support base continues to shrink,” said Mark P. Jones, chairman of political science department at Rice University. “The GOP is going to have to address that support over the next few years, particularly as they approach the next presidential election.”

Considering the deep divisions in the electorate, 2012 could easily be called “the year of the gap.”

There was the gender gap. Women favored Obama, 55 percent to 44 percent, while men chose Romney by 52 percent to 45 percent. Mothers were more likely to support Obama (56 percent to 43 percent), while fathers sided with Romney (53 percent to 45 percent).

“Democrats effectively made the case that issues important to women, not just issues like abortion and reproductive rights but economic issues of equal pay and access to jobs, those issues resonated with women,” said Ron Schurin, a political scientist at the University of Connecticut. “The Romney campaign seemed at times to be tone deaf on those issues. They tried to make a case, they just didn’t do it effectively.”

In addition to the gender gap, there was a yawning generation gap. Voters under the age of 30 were strongly pro-Obama, 59 percent to 37 percent, while voters 65 and older favored Romney by 57 percent to 43 percent.

Angry Republican conservatives say they the only way to rebuild a majority is to purge the party of its old-fashioned pragmatists like Romney.

“Tomorrow morning we launch the battle for the heart and soul of the Republican Party between small government constitutionalists and Tea Party types, and those like George Bush and Karl Rove who want to expand government,” veteran conservative activist Richard A. Viguerie, chairman of ConservativeHQ.com.

Summer Ballentine of the Hearst Washington bureau contributed to this report.